Joseph R. Stern

A role of acetoacetyl-CoA synthetase in acetoacetate utilization by rat liver cell fractions

Abstract The enzyme acetoacetyl-CoA synthetase which catalyzes the synthesis of acetoacetyl-CoA from acetoacetate, CoA and ATP is shown to be present in mitochondrial and cytoplasmic fractions of rat liver. It was decreased in both specific activity and amount after starvation for 48 hours. It is proposed that the synthetase normally functions in the re-utilization of some of the acetoacetate produced within the mitochondrion as well as that reaching the cytoplasm, and that acetoacetate can function as an acetyl carrier between mitochondria and cytoplasm.

Studies of citrate transport in Aerobacter aerogenes: binding of citrate by a membrane bound oxalacetate decarboxylase.

Abstract Citrate is a competitive inhibitor of the Na + -activated oxalacetate (OAA) decarboxylase, a membrane-bound enzyme participating in citrate catabolism by Aerobacter aerogenes . It is proposed that this OAA decarboxylase also functions as a carrier protein in the transport of citrate by a novel mechanism.

Reversal of the stereospecificity of the citrate synthase of Clostridiumkluyveri by p-chloromercuribenzoate☆

Abstract The stereospecificity of citrate synthase in extracts of Clostridium kluyveri (Barker strain) can be changed reversibly from the (R)-type to the (S)-type by treatment with p-chloromercuribenzoate. It is proposed that sulfhydryl groups are essential for the (R)-type stereospecificity of the enzyme and their incomplete oxidation or reduction accounts for mixed labelling patterns in citrate.

The enzymic hydrolysis of glutathione thioesters

Abstract The enzyme-catalyzed hydrolysis of S -lactoyl-, S -acetyl-, S -acetoacetyl-, S -(β-hydroxy-β-methylglutaryl)- and S -succinylglutathione has been examined in beef liver. Purification studies have revealed that a single enzyme is involved, namely, glyoxalase II. A reversible non-enzymic transfer of the acetoacetyl moiety of acetoacetyl-coenzyme A and acetoacetyl-pantetheine to glutathione was found to occur at alkaline pH.

Enzymic carboxylation of butyryl coenzyme A. I. Conversion of butyryl coenzyme A to 2-ethylmalonyl coenzyme A☆

Abstract 1. 1. The presence of an enzyme in dog skeletal and heart muscle and ox, chicken, and rat liver, which catalyzes the fixation of C 14 O 2 by butyryl coenzyme A (CoA) is described. The reaction requires adenosine triphosphate (ATP) and Mn ++ or Mg ++ . 2. 2. The relative rates of carboxylation of acetyl-CoA, propionyl-CoA, and butyryl-CoA in these tissues is about 1:25:3, suggesting that one enzyme—propionyl-CoA carboxylase—is involved in all three reactions. In rat liver mitochondria the rates of carboxylation of propionyl-CoA and butyryl-CoA are almost equal. 3. 3. The product of carboxylation of butyryl-CoA has been identified as 2-ethyl-malonyl-CoA. Reversibility of the carboxylation reaction was demonstrated with synthetic 2-ethylmalonyl-CoA. 4. 4. Rat liver mitochondrial extract catalyzes the synthesis of 2-ethylmalonyl-CoA from 2-ethylmalonate, adenosine triphosphate and coenzyme A. 5. 5. Methylmalonyl-CoA isomerase preparations from kidney and Propionibacterium shermanii do not isomerize 2-ethylmalonyl-CoA to either glutaryl-CoA or methylsuccinyl-CoA. 6. 6. The significance of the butyryl-CoA carboxylation reaction and the metabolism of 2-ethylmalonyl-CoA are discussed.

Failure of ethylenediaminetetraacetate or manganese to affect (R)‐citrate synthesis in Clostridium kluyveri and Clostridium cylindrosporum

Extracts of several obligate anaerobes [l-3] possess the unusual property of synthesizing (R&citrate from oxalacetate and acetyl-CoA, i.e. the opposite enantiomer to that synthesized by pig heart citrate synthase, namely (

Enzymes of ketone body metabolism. II.Properties of an acetoacetate-synthesizing enzyme prepared from ox liver.

)-citrate. We have shown [4] that the (R)type stereospecificity of the citrate synthase present in extracts of Clostridium kluyveri (Barker) was exhibited only under reducing conditions and that oxidizing conditions caused a significant increase in the amount of (Q-citrate formed. The stereospecificity of the C. kluyveri synthase could also be changed, in a reversible manner, from the (R)-type to the (S)-type by treatment with p-chloromercuribenzoate. Similar changes have been demonstrated in extracts of Clostridium acidi-urici and Clostridium cylindrosporum [S]. Gottschalk [6] has partly purified a sulfhydryl enzyme (“(RR)-citrate synthase”) from C. acidi-urici which forms (R)-citrate under reducing conditions. This enzyme was inhibited by ethylenediaminetetraacetate (EDTA) and stimulated specifically by Mn++ among several divalent cations tested. This paper demonstrates that (R)-citrate synthesis by extracts of C. kluyveri and C. cylindrosporum is not sensitive to EDTA or to Mn++. Thus no correlation exists between the capacity to synthesize (R)-citrate and sensitivity to these agents. 2. Materials and methods